[APML]: Piggy-back camera lens

[Andrew.Martyn@dao.defence.gov.au]

The Astro-Photography Mailing List
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Hi ,I'm new to this list and seeing all the flaming that has been going on
about content, I'm a bit wary about posting to this list as I'm very much a
beginner. A bit of background is that I'd tried some astrophotography some
years ago using an old totally manual Praktica (?) SLR camera with a 50mm
1.8 lens. Took some OK piggy back shots and some bad to terrible prime and
eyepiece projection shots. Have just built myself a new rigid mount for
which I built a reasonable PEC electronic drive and I am now contemplating
trying astrophotography again. To get into the groove of things I thought
I'd start out buying a second hand lens in the 135-300mm range and do some
piggy-back shots.

Now for the questions. Bear in mind that I'm not after fantastic results,
just shots that look good to me on a 6" x 4" photo without to much
examination. If I enjoy taking these photos, then I'll look at stepping up
to something better.

1.   I assume a fixed lens performs better than a zoom lens of the same
price? Should I stay away from a zoom lens entirely?

2.   My camera has a screw mount, can you buy an adapter to take any other
type of lens? I'd assume that inserting an adapter will effect the focus
position, is this a problem?

3.   I know there are lots of trade offs between focal length, aperture,
focal ratio, size of field, and exposure length, which I can work out for
myself, but I assume that for a given price, a longer focal ratio lens (ie
f 4) is going to distort the image less than a shorter focal lens (ie f
2.8)?

4.   What is the field size for 35mm film using a 200mm lens? I can then
work out the sizes for the other focal lengths.

5.   I had a look on the net at a dealer who sells second hand lenses and
the list is mind boggling. There are brand names I've never heard of and I
imagine even with the same brand, quality has varied over time. Is there
any particular rules I should follow and things I should look for, or
should I just trust the dealer? For interest, this is my list of possibles
I selected (all prices are in Australian $, to convert to US$ divide by
1.6):

Canon 300mm f4 FD $150
Canon 135mm f3.5 $69
Pentax 135mm f2.5 $80
Pentax 200mm f4 $189
Pentax 150mm f4 $150
Nikon 200mm f4 $195
Vivitar 200mm f3.5 $89
Fujica 200mm f4.5 (screw) $99
Konica Hexanon AR 135mm f3.2 $149
Pentacon 135mm f2.8 (screw) $60
Rikenon 135mm f2.8 (screw) $60
Sigma 135mm f2.8 $110
Sigma 200mm f3.5 $39
Soligor 153mm f2.8 (screw) $45
Tamron 200mm f3.5 $88
Tamron 200mm f3.5 (universal) $165
Tamron 300mm $100
Ambassador 135mm f2.8 (screw) $45

Andy
Canberra
Australia